Redundant bus fault detection

ABSTRACT

A system and method for an approach of detecting faults in a redundant bus system based upon four timers.

FIELD OF THE INVENTION

This application relates to the field of system bus communication, andparticularly to fault detection in a redundant bus building automationsystem.

BACKGROUND

Numerous regulatory agencies dealing with building safety haveestablished different safety classifications for different electricalcircuits and communication transmission pathways. The highest level ofsafety class is “class X” (see 12.3.6 NFPA 72 2010 safety regulation).In order to obtain a “class X” classification, the followingrequirements must be meet:

-   -   All circuits have a redundant path.    -   Circuit paths between the Fire Alarm Central Unit (FACU) and        remote peripherals shall continue to operate flawlessly under        the condition of a single open or a single short circuit        condition.    -   Circuit paths shall be monitored and supervised to detect and        annunciate a short or open circuit condition.        Thus, FACU and remote peripherals must be monitored and any        short or open circuit conditions must be annunciated in order to        fulfill the requirements of the “class X” performance criteria.

As redundant circuits are typically routed via different physicaltransmission pathway locations for the obvious safety reasons; thepropagation delays experienced on one pathway versus another will vary.Real world cable propagation delays of five nanoseconds per meter ormore preclude a simple solution of combinatorial logic being implementedon the redundant received data lines of the two pathways to arrive at adesired logic level for the desired bit time.

Currently, simplistic approaches have been used to detect open or shortconditions in a circuit. Such approaches detected the fault and providedlittle or no additional information. In a fire or disaster, additionalinformation enables first responders to better understand where problemsor dangers may exist. Maintainers of a redundant bus system may alsobenefit from additional information when an error is detected in asystem and more quickly correct detected faults. Therefore, there is aneed for an approach that not only detects a short or open circuit, butprovides additional information that may aid in correcting the fault oridentifying at risk areas during an emergency.

SUMMARY

In accordance with one embodiment of the disclosure, there is provided amethod of monitoring redundant communication buses using timers toassure at least one data path exists to physical units from acontroller.

The above described systems, methods, features and advantages of thepresent invention, as well as others, will become more readily apparentto those of ordinary skill in the art by reference to the followingdetailed description and accompanying drawings. While it would bedesirable to provide an automated Demand Response system that providesone or more of these or other advantageous features, the teachingsdisclosed herein extend to those embodiments which fall within the scopeof the appended claims, regardless of whether they accomplish one ormore of the above-mentioned advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.In the figures, like reference numerals designate corresponding partsthroughout the different views.

FIG. 1 shows a block diagram of redundant buses with fault detectionapproach that connects a fire alarm central unit (FACU) and remoteperipherals in accordance with an example implementation;

FIG. 2 a depicts flow diagrams of timers implemented in the redundantbus with fault detection approach of FIG. 1 in accordance with anexample implementation.

FIG. 2 b depicts a flow diagram of the redundant bus with faultdetection approach which makes use of the timers of FIG. 2 a inaccordance with an example implementation.

FIG. 2 c depicts a continuation of the flow diagram of FIG. 2 b inaccordance with an example implementation.

FIG. 2 d depicts a continuation of the flow diagram of FIGS. 2 b and 2 cin accordance with an example implementation.

FIG. 2 e depicts a continuation of the flow diagram of FIG. 2 b-2 d inaccordance with an example implementation.

FIG. 2 f depicts a continuation of the flow diagram of FIG. 2 b-2 e inaccordance with an example implementation.

DESCRIPTION

An approach for a redundant communication bus having fault detection,annunciation, and mitigation within a building is described. Withreference to FIG. 1, a block diagram 100 of redundant buses 102, 104with fault detection approach that connects a fire alarm central unit(FACU) 106 and remote peripherals 108, 110, and 112 in accordance withan example implementation. The FACU 106 may have a bus controller, suchas a Controller Area Networking (CAN) bus controller 114 and FAIL lightemitting diodes (LEDs) 116. The FAIL LEDs 116 indicate if an error orfault has been detected in the FACU 106 or communication buses 102 and104. The LED is a visual indicator. In other implementations, differentor additional visual and audio indicators may be employed. For example,mechanical flags, incandescent light bulbs, alarms, bells, etc. In yetother implementations, a less desirable approach of having a singlevisual indicator to identify a fault on one of the redundant buses maybe implemented rather than an LED associated with each type of error oneach bus.

The CAN bus controller 114 is a multi-master broadcast serial busapproach for connecting remote peripherals 108, 110, and 112 with FACU(106) and each other. Each remote peripheral 108, 110, and 112, is ableto send and receive messages, but not simultaneously. A message mayconsist of an ID (identifier), which represents the priority of themessage, and up to eight data bytes. It is transmitted serially onto thebus. This signal pattern may be encoded in non-return-to-zero (NRZ) andis sensed by all nodes.

The remote peripherals that are connected by a bus are typicallysensors, actuators, and other control devices. These devices may not beconnected directly to the bus, but through a host processor. If the busis free, any remote peripheral or controller may begin to transmit. Iftwo or more remote peripherals or controllers begins sending messages atthe same time, the message with the more dominant ID (which has moredominant bits, i.e., zeroes) may overwrite other nodes' less dominantIDs, so that eventually (after this arbitration on the ID) only thedominant message remains and is received by all nodes. This mechanism istypically referred to as priority based bus arbitration or morespecifically Carrier Sense Multiple Access with collision detection.Messages with numerically smaller values of IDs have higher priority andare transmitted first.

Each remote peripheral may require a host processor that decides whatreceived messages mean and which messages it wants to transmit itself.The sensors, actuators, and control devices are typically connected tothe host processor. When receiving, the CAN controller may storereceived bits serially from the bus until an entire message isavailable, which can then be fetched by the host processor (usuallyafter the CAN controller has triggered an interrupt). When sending, thehost processor stores it's transmit messages to a CAN controller, whichtransmits the bits serially onto the bus.

A CAN bus transceiver is able to transmit and receive messages,typically which it receives\sends from\to the node's microcontroller.When receiving, the transceiver adapts differential signal levels fromthe bus to levels that the CAN controller expects and may haveprotective circuitry that protects the CAN controller. Whentransmitting, the transceiver converts the transmit-bit signal receivedfrom the CAN controller into a differential signal that is sent on thebus.

Typically, bit rates up to 1 Mbit/s are possible at network lengthsbelow 40 m. But, by decreasing the bit rate, longer network distances(e.g., 500 m at 125 kbit/s) may be achieved. Note: we limit at about 500m at 50 kbit/s. The CAN data link layer protocol is standardized in ISO11898-1 (2003). This standard describes mainly the data link layer(composed of the logical link control (LLC) sub-layer and the mediaaccess control (MAC) sub-layer) and some aspects of the physical layerof the OSI reference model. All the other protocol layers are typicallynetwork or implementation specific.

By timing different aspects of bus signals, such as the redundant CANbus shown in FIG. 1, the “health” of the bus may be ascertained andensure that the delivered signal is able to be delivered between theFACU 106 and all remote peripherals 108, 110, and 112. In the currentexample implementation, four timing parameters may be qualified andinspected by the bus controller (CAN bus controller 114). Each of thetiming parameters may be unique to an individual system and the timevalue for each may be tailored to that system or installation. The fourtiming parameters are (1) power up/cold start reset, (2) periodicactivity, (3) valid bit time, and (4) maximum pathway delay.

Turning to FIG. 2 a, flow diagram 200 of timer parameters 202, 204, 206,and 208 implemented in the redundant bus with fault detection approachof FIG. 1 in accordance with an example implementation is depicted.Timer parameter 1 202 is associated with a power up/cold start time ofthe controller and is the time period from power up until bus activityoccurs. A finite time delay exists that a FACU 106 requires before thefirst activity on the bus is initiated by the CAN bus controller 114. Inthe current example, the time is set to a predetermined value of 20seconds for Timer_(—)1.

The value for Timer_(—)1 may be determined via monitoring the power-upof the FACU 106 or by use of other times that prevent activities duringpower up initialization of FACU or (108), (110), (112). The Timer_(—)1may be preset with a 20 second value 210 and enabled via an enableTimer_(—)1 signal 212. Upon expiration of Timer_(—)1, a Timer_(—)1expiration signal or message may be triggered 214. If Timer_(—)1 hasexpired and no activity has occurred on the bus, then the bus may bedeclared faulty. If redundant buses are present, and the other bus isnot faulting, then messaging may be routed over the non-faulting bus.

The value of Timer_(—)2 204 may be preset 216 to 110 milliseconds in theexample. This time may be set for a margin of error just above themaximum typically expected CAN redundant bus traffic within a givenimplementation. In the current example, the FACU “pings” all its nodesto check for a response periodically. If a node does not acknowledge itsaddress specific “ping,” the FACU knows there is a problem with thatperipheral. If the embodiment detects that the typically periodic pingtime is exceeded, it knows that a fault condition exists and handlesaccordingly. The 110 milliseconds (mS) may be determined to be athreshold that some bus activity from a remote peripheral should occuror that the FACU has an error in not sending out the typically periodic“ping”. If no bus activity occurs during the 110 mS once the Timer_(—)2is enabled 218, then the remote peripheral or FACU is no longercommunicating using that bus and communication should occur over theredundant bus. Upon expiration of Timer_(—)2, a Timer_(—)2 expirationsignal may be generated 220. The value of 110 mS is set as a constantupper threshold of silence on the bus in the current example, but inother implementations the value may be different and be determined bytypical system traffic parameters in the redundant bus implementation.In yet other implementations, a controller, may keep track of themaximum time between reception of a message from a peripheral devicethat is less than a hard coded maximum and preset Timer_(—)2 216 withthat value.

The third timer timer_(—)3 206 is a valid bit timer and is associatedwith the typical single “bit” time of the installed redundant CAN bussystem. The valid bit timer is used to verify that the “bit” time is nottoo short (e.g. for 50 Kbits/sec a bit time is approx 20 μSec); so ifTimer_(—)3 expires true, a condition of error in the form of aconcatenated bit time was not experienced. Each of the redundant busesis typically set at one speed in bits per second and remains at thatspeed. The speed is inversely proportional to the bit time, and mayactually be 1/bit time. For example, in the case of the Siemens SII SBTCAN Bus, a transmission speed of fifty Kilobits per second isuniversally deployed in product offerings. This results in an individualbit time of twenty microseconds (20 μSec; or 20×10⁻⁶ seconds). The CANbus controller monitors each bit time and insures that it exceeds theminimum threshold of fifteen microseconds (15 μSec; or 15×10⁻⁶ seconds).In the case of one leg of the differential redundant bus being cut;logic transitions may occur however they will be short “spikes” farbelow the valid bit time in duration. Therefore in the case of a lessthan valid bit time is detected, the CAN bus controller may detect thisfault, annunciate it, and ensure the connection of a valid functioningpathway between the Cabinet and Remote Circuit Node(s). Therefore in thecurrent example, a predetermined value of 15 mS may be used as aconstant lower limit threshold; but this value may be a user configuredvalue in other implementations. Or in yet other implementations, thevalue may be a “constants” loaded by the CAN bus controller at power up.In the current example, the value of Timer_(—)3 may be preset 222 (15 mSin the current example) and enabled by signal 224. Upon expiration ofTimer_(—)3, a Timer_(—)3 expire signal may be generated 226.

The fourth timer Timer_(—)4 208 is associated with the cable propagationdelay and is the maximum pathway delay. In a redundant bus system ofknown maximum cable pathway wire distances, it may be assumed that themaximum possible pathway differential between the redundant pathways maybe given a propagation delay of approximately 5 nanoseconds per meter;the typical worst case delay between the pathway upon which the “1^(st)bit even” is experienced and the subsequent “longer length” pathway. TheCAN bus controller may initially select the first valid bus by way offirst activity. The first valid bus provides connectivity between thecabinet and Remote Nodes on that specific bus. As there typically willbe a maximum bus cable length and a maximum delay time per unit lengthof cable (e.g. five nanoseconds per meter), the CAN bus controller mayascertain a maximum expected delay time for bus activity to appear onthe “longer” bus pathway. In the current example, if a maximum cablelength of 300 meters is projected for one of the redundant buses andassuming a maximum transmission line propagation delay of 5 nS permeter, and adding in the propagation delay for a typical bus physicallayer transceiver, a value of two microseconds (2 μSec or 2×10⁻⁶Seconds) may be determined as the maximum “lag” time that the longer buspathway should exhibit compared with the first detected shorter buspathway. Therefore, a value of two microseconds (2 μSec) may be used asa constant upper limit threshold. In other implementations, this valuemay be a user configured value for different systems. In yet otherimplementations, a value for this timer may be treated like other“constants” loaded by a master microcontroller at power up that couldascertain the correct applicable “constant” value. The value ofTimer_(—)4, the maximum pathway delay, may be preset 228 (2 mS in thecurrent example) and enabled by signal 230. Upon expiration oftimer_(—)4, a Timer expire signal may be generated 232.

Upon cold start/reset 250, the timers of FIG. 2 a are initialized withtheir preset values. All CAN bus pathway FAIL LEDs may be extinguished252. Redundant bus 1 (CAN bus pathway 1) peripherals may be enabledwhile redundant bus 2 (CAN bus pathway 2) peripherals may be disabled254. The cold start timer “Timer_(—)1” 202 is also enabled 256. In thecurrent example implementation, the terms “disabled” means to make theCAN bus pathway as a background secondary or non-primary pathway (ifthere are no faults present). The term “enable” means to make the CANbus pathway the primary pathway.

A determination is made if a bit is detected on CAN bus pathway 1 258and similarly on CAN bus pathway 2 260. If no bits have been detected,then a check is made if Timer_(—)1 has expired 262. If Timer_(—)1 hasnot expired, the bus pathway 1 and bus pathway 2 are checked again tosee if a bit has been detected 258 and 260. If Timer_(—)1 has expired262, then the CAN pathway 1 and 2 FAIL LEDs may be illuminated 264 andsteps 254 and 256 may be repeated.

In FIG. 2 c, a continuation of the flow diagram of FIG. 2 b inaccordance with an example implementation is depicted. If in FIG. 2 b, abit is detected on CAN bus pathway 2, then Timer_(—)1 is reset 292 andCAN bus pathway 1 is disabled and CAN bus pathway 2 is enabled 294.Timer_(—)2, Timer_(—)3 and Timer_(—)4 are also enabled at this time 296and the flow continues to FIG. 2 d.

Turning to FIG. 2 d, a continuation of the flow diagram of FIGS. 2 b and2 c in accordance with an example implementation is depicted. After thetimers (Timer_(—)2, Timer_(—)3, and Timer_(—)4) have been activated 296FIG. 2 c, a determination is made if another bit is detected on CAN buspathway 2 308. If a bit is detected on CAN bus pathway 2 308, thenTimer_(—)2 is reset 302. A check is then made if Timer_(—)3 has expired306. If Timer_(—)3 has expired, then Timer_(—)3 is reset 304 and one ofthe two inputs into AND function 300 is set. If Timer_(—)3 has notexpired 306, then Timer_(—)3 is reset 314 and one of two inputs to “OR”function 316 is set.

Furthermore, after the timers (Timer_(—)2, Timer_(—)3, and Timer_(—)4)have been activated 296 FIG. 2 c a determination is made if CAN buspathway 1 has activity 320, where “1->0 or 0->1” means either a bittransition of dominant to recessive or recessive to dominant activity.If there is activity on CAN pathway 1 320, then the CAN bus pathway 1FAIL LED is extinguished 322 and an input to “OR” function 324 may beset. If there is no activity on CAN bus pathway 1, 320 and Timer_(—)4has expired, then CAN bus pathway 1 FAIL LED is illuminated 328 and asecond input to the “OR” function 324 may be set. Otherwise, if there isno activity on CAN bus pathway 1 320 and Timer_(—)4 has not expired 326,then a check is again made for activity on CAN bus pathway 1 320. Ifeither of the inputs to the “OR” function is set, then the secondcondition for “AND” function 300 is set.

If no bit is detected on CAN bus pathway 2 308 and Timer_(—)2 has notexpired 310, then CAN bus pathway 2 is again checked for RxD 1->0. IfTimer_(—)2 has expired 310, then Timer_(—)3 is reset 312 and a secondcondition to “OR” function 316 is set. If either condition of “OR”function 316 is set, then CAN bus pathway 2 FAIL LED is illuminate. Ifboth condition of “AND” function 300 are set, then Timer_(—)2 is enabled284 FIG. 2 c and a determination is made if a bit is detected on CAN buspathway 2 280. If a bit is detected on CAN bus pathway 2 280, thenTimer_(—)2 is reset 286 and the CAN bus pathway 2 FAIL LED isextinguished 288. Timers Timer_(—)2, Timer_(—)3, and Timer_(—)4 may thenbe enabled 296 and processing continues in FIG. 2 d. Otherwise if CANbus pathway 2 bit is not detected 280 and Timer_(—)2 is expired 282,then CAN bus pathway 2 FAIL LED is illuminated 290 and Timer_(—)2 isreset 298 and processing continues at 362, FIG. 2 e. If Timer_(—)2 hasnot expired 282, then CAN bus pathway 2 is checked again for a bit 280.

Turning to FIG. 2 e, a continuation of the flow diagram of FIG. 2 b-2 din accordance with an example implementation is depicted. Timer_(—)1 isreset 360 after a bit has been detected on CAN bus pathway 1 258 FIG. 2b. The CAN bus pathway is enabled and CAN bus pathway 2 is disabled 362.Timer_(—)2, Timer_(—)3, and Timer_(—)4 are enabled 364 and checks aremade for activity on CAN bus pathway 2 372. If CAN bus pathway 2 hasactivity, then CAN bus pathway 2 FAIL LED is extinguished 374 and acondition is set for “OR” function 380. Otherwise, if CAN bus pathway 2activity is not detected 372 a check is made if Timer_(—)4 has expired376. If Timer_(—)4 has not expired 376, then CAN bus pathway 2 ischecked for activity again 372. Otherwise if Timer_(—)4 has expired 376,then CAN bus pathway 2 FAIL LED is illuminated 378 and the secondcondition is set on “OR” function 380.

In FIG. 2 f, a continuation of the flow diagram of FIG. 2 b-2 e inaccordance with an example implementation is depicted. Once Timer_(—)2,Timer_(—)3, and Timer_(—)4 have been enabled 364 FIG. 2 e, a check ismade on CAN bus pathway 1 to determine if a bit has been detected 400.If a bit has been detected on CAN bus pathway 1, Timer_(—)2 is reset 402and a check is made if Timer_(—)3 has expired 408. If Timer_(—)3 hasexpired 408, then Timer_(—)3 is reset 410 and the first condition of the“AND” function 412 is set. If Timer_(—)3 has not expired 408, thenTimer_(—)3 is reset 414 and the first condition of the “OR” function 418is set.

If a bit is not detected on CAN bus pathway 1 400, then a check is madeto determine if Timer_(—)2 has expired 406. If Timer_(—)2 has notexpired 406, then the CAN bus pathway 1 is checked again 400. IfTimer_(—)2 has expired 406, then Timer_(—)2 is reset 416 and the secondcondition of an “OR” function 418 is set. If either condition of “OR”function 418 is set, then CAN bus pathway 1 FAIL LED is illuminated 419.

Furthermore, if either condition of “OR” function 380 FIG. 2 e are set,then Timer_(—)4 420 FIG. 2 f is reset and the second condition of “AND”function 412 is set. If both conditions of the “AND” function 410 areset, then Timer_(—)2 is enabled 358 FIG. 2 e and a determination if abit has been detected on CAN bus pathway 1 is made 352.

If a bit is detected on CAN bus pathway 1 352, then Timer_(—)2 is reset368 and the CAN bus pathway 1 FAIL LED is extinguished 370 andTimer_(—)2, Timer_(—)3, and Timer_(—)4 are enabled 364. If a bit is notdetected on CAN bus pathway 1 352, then a check of expiration ofTimer_(—)2 is made 354. If Timer_(—)2 has not expired 354, then the CANbus pathway 1 is again checked for a bit 352. Otherwise, if Timer_(—)2has expired, 354 CAN bus pathway 1 FAIL LED is illuminated 356 andTimer_(—)2 is reset 350. After Timer_(—)2 is reset 350, then CAN buspathway 2 is enabled and CAN bus pathway 1 is disabled 294 FIG. 2 c.Similarly if CAN bus pathway 1 FAIL LED is illuminated 419, then CAN buspathway 2 is enabled and CAN bus pathway 1 is disabled 294.

The immediate annunciation of a fault detection and continuousmonitoring of bus health of the redundant CAN bus pathways inherentlyprovides additional information to managers of Building Technologysafety logistics. Additional information in the immediate detection offaults such as accidently cut wire paths (i.e. miscellaneousconstruction activity such as drilling through a sheet rock wall) may beidentified and rectified before time of emergency. A simple cold start“power up” system check may be routinely performed to verify the healthof BOTH CAN bus pathways and provide managers of Building Technologysafety the ease of mind from the additional information that theredundant CAN bus pathways are both fully operational BEFORE anemergency condition occurs. The system also provides the FACU additionalinformation which in turn may be provided to Building Technologiessafety management personnel. Should some circuit failure occur betweencertain nodes of the pathway, the FACU may quickly sequentially ping thenodes from nearest to most distant and identify the exact geographicallocation area of the fault by observing the last successful response toa ping and the first failed response. This additional informationprecludes the need of physically examining the entire circuit pathway toidentify the exact location of the short or open circuit condition.Finally, should one pathway fail during an emergency prior to other fireor smoke detector modules, additional information in the form of knowingthe regional geographic core of a possible emergency (i.e. fire within awall(s) which has not yet caused a smoke detector to trip) and thisadditional information allows Building Technology safety managementpersonnel to more efficiently evacuate personnel and\or valuableproperty.

The foregoing detailed description of one or more embodiments of theautomated demand response system has been presented herein by way ofexample only and not limitation. It will be recognized that there areadvantages to certain individual features and functions described hereinthat may be obtained without incorporating other features and functionsdescribed herein. Moreover, it will be recognized that variousalternatives, modifications, variations, or improvements of theabove-disclosed embodiments and other features and functions, oralternatives thereof, may be desirably combined into many otherdifferent embodiments, systems or applications. Presently unforeseen orunanticipated alternatives, modifications, variations, or improvementstherein may be subsequently made by those skilled in the art which arealso intended to be encompassed by the appended claims. Therefore, thespirit and scope of any appended claims should not be limited to thedescription of the embodiments contained herein.

What is claimed is:
 1. A building automation system, comprising: a first communication bus having a first pathway with a first propagation delay; a second communication bus having a second pathway with a second propagation delay, where the second pathway is redundant to the first pathway and the first propagation delay is different from the second propagation delay; a bus controller coupled to at least one peripheral device by the first communication bus and the second communication bus and where a first timer is associated with a time period from power up until activity occurs on each of the first communication bus and the second communication bus; and an at least one visual indicator that is associated with expiration of the first timer when activity is not detected and at least one of the first communication bus or second communication bus being deactivated in response to the expiration of the first timer.
 2. The building automation system of claim 1, where the first communication bus and second communication bus are controller area networking (CAN) buses.
 3. The building automation system of claim 1, where the at least one of the first communication bus or second communication bus being deactivated is making that at least one of the first communication bus or second communication bus a non-primary communication bus.
 4. The building automation system of claim 1, where the first timer is set to a first predetermined value.
 5. The building automation system of claim 3, where the first predetermined value of 20 seconds.
 6. The building automation system of claim 1, were the at least one visual indicator is a light emitting diode.
 7. A building automation system, comprising: a first communication bus having a first pathway with a first propagation delay; a second communication bus having a second pathway with a second propagation delay, where the second pathway is redundant to the first pathway and the first propagation delay is different from the second propagation delay; a bus controller coupled to at least one peripheral device by the first communication bus and the second communication bus and where a first timer is associated with a periodic ping on each of the first communication bus and the second communication bus; and an at least one visual indicator that is associated with expiration of the first timer when a response to the periodic ping is not detected and at least one of the first communication bus or second communication bus being deactivated in response to the expiration of the first timer.
 8. The building automation system of claim 7, where the first communication bus and second communication bus are controller area networking (CAN) buses.
 9. The building automation system of claim 7, where the at least one of the first communication bus or second communication bus being deactivated, is making at least one of the first communication bus or second communication bus a non-primary communication bus.
 10. The building automation system of claim 7, where the first timer is set to a first predetermined value.
 11. The building automation system of claim 10, where the first predetermined value of 110 milliseconds.
 12. The building automation system of claim 7, were the at least one visual indicator is a light emitting diode.
 13. A building automation system, comprising: a first communication bus having a first pathway with a first propagation delay; a second communication bus having a second pathway with a second propagation delay, where the second pathway is redundant to the first pathway and the first propagation delay is different from the second propagation delay; a bus controller coupled to at least one peripheral device by the first communication bus and the second communication bus and where a first timer is associated with a bit time on each of the first communication bus and the second communication bus; and an at least one visual indicator that is associated with the first timer when a bit is detected prior to expiration of the first timer and at least one of the first communication bus or second communication bus being deactivated in response to the bit being detected prior to expiration of the first timer.
 14. The building automation system of claim 13, where the first communication bus and second communication bus are controller area networking (CAN) buses.
 15. The building automation system of claim 13, where the at least one of the first communication bus or second communication bus being deactivated, is making at least one of the first communication bus or second communication bus a non-primary communication bus.
 16. The building automation system of claim 13, where the first timer is set to a first predetermined value.
 17. The building automation system of claim 16, where the first predetermined value of 110 milliseconds.
 18. The building automation system of claim 13, were the at least one visual indicator is a light emitting diode.
 19. A building automation system, comprising: a first communication bus having a first pathway with a first propagation delay; a second communication bus having a second pathway with a second propagation delay, where the second pathway is redundant to the first pathway and the first propagation delay is different from the second propagation delay; a bus controller coupled to at least one peripheral device by the first communication bus and the second communication bus and where a first timer is associated with a periodic ping on each of the first communication bus and the second communication bus; and an at least one visual indicator that is associated with expiration of the first timer when a response to the periodic ping is not detected and at least one of the first communication bus or second communication bus being deactivated in response to the expiration of the first timer.
 20. The building automation system of claim 19, where the first communication bus and second communication bus are controller area networking (CAN) buses.
 21. The building automation system of claim 19, where the at least one of the first communication bus or second communication bus being deactivated, is making at least one of the first communication bus or second communication bus a non-primary communication bus.
 22. The building automation system of claim 19, where the first timer is set to a first predetermined value.
 23. The building automation system of claim 22, where the first predetermined value of 15 microseconds.
 24. The building automation system of claim 19, were the at least one visual indicator is a light emitting diode.
 25. A building automation system, comprising: a first communication bus having a first pathway with a first propagation delay; a second communication bus having a second pathway with a second propagation delay, where the second pathway is redundant to the first pathway and the first propagation delay is different from the second propagation delay; a bus controller coupled to at least one peripheral device by the first communication bus and the second communication bus and where a first timer is associated with a difference between the first propagation delay and the second propagation delay with the first timer being activated upon receipt of a first message on the first communication bus; and an at least one visual indicator that is associated with expiration of the first timer prior to receipt of the first message on the second communication bus and the second communication bus being deactivated in response to the expiration of the first timer.
 26. The building automation system of claim 25, where the first communication bus and second communication bus are controller area networking (CAN) buses.
 27. The building automation system of claim 25, where the first timer is set to a first predetermined value.
 28. The building automation system of claim 25, where the first predetermined value of 15 microseconds.
 29. The building automation system of claim 25, were the at least one visual indicator is a light emitting diode.
 30. A building automation system, comprising: a first communication bus having a first pathway with a first propagation delay; a second communication bus having a second pathway with a second propagation delay, where the second pathway is redundant to the first pathway and the first propagation delay is different from the second propagation delay; a bus controller coupled to at least one peripheral device by the first communication bus and the second communication bus, and the bus controller includes: a first timer is associated with a time period from power up until activity occurs on each of the first communication bus and the second communication bus where an at least one visual indicator which is activated with expiration of the first timer when activity is not detected and at least one of the first communication bus or second communication bus being deactivated in response to the expiration of the first timer; a second timer associated with a periodic ping on each of the first communication bus and the second communication bus where the at least one visual indicator is activated with expiration of the second timer when a response to the periodic ping is not detected and where at least one of the first communication bus or second communication bus being deactivated in response to the expiration of the second timer; a third timer is associated with a periodic ping on each of the first communication bus and the second communication bus and the at least one visual indicator is activated with expiration of the first timer when a response to the periodic ping is not detected and where at least one of the first communication bus or second communication bus being deactivated in response to the expiration of the third timer; and a fourth timer is associated with a difference between the first propagation delay and the second propagation delay with the fourth timer being activated upon receipt of a first message on the first communication bus and where the at least one visual indicator is activated upon expiration of the fourth timer prior to receipt of the first message on the second communication bus and the second communication bus being deactivated in response to the expiration of the first timer. 